Transcript 04 Toward Carbon Based Electronics.2

Graphene FET: High Saturation Velocity
Meric, Han, Young, Kim, and Shepard (2008)
Saturation velocity
Vtop = -3 V
0.8
Vtop = -1.5 V
Vtop = 0 V
VtopDirac
= 2 V @ Vg = -40 V
vsat (108 cm/s)
Vtop = -2 V
vsat  vF
0.6
0.4

EF
0.2
0.0
0.0
0.1
0.2
0.3
0.4
EF (eV)
For comparison:
vFermi = 1x108 cm/s
Silicon: 1x107 cm/s
GaAs: 0.7x107 cm/s
1
vdrift  ( mE ) 1  vsat
1
Operation current density > 1 mA/mm
0.5
Graphene Device Fabrication
• Developing Graphene Nanostructure Fabrication Process
graphene
Contacts:
PMMA
EBL
Evaporation

Graphene patterning:
HSQ
EBL
Development
Graphene etching:
Oxygen plasma
Local gates:
ALD HfO2
EBL
Evaporation
Graphene device
structure with local
gate control
Oezyilmaz, Jarrilo-Herrero and Kim APL (2007)
Graphene Nanostructures
Quantum Dot
Geim (Manchester)
Graphene nanoribbons
& nanoconstrictions
AB Ring
Morpurgo (DELFT)
Goldhaber-Gordon (Stanford)
Graphene PN junctions
Graphene Side Gates
Ensslin (ETH)
Kim (Columbia)
Graphene with local barrier
Marcus (Harvard)
Graphene Nanoribbons: Confined Dirac
Particles
Gold electrode
Graphene
Dirac Particle Confinement
W
ky 
3 
W
ky 
2 
W
ky 
1 
W
W
1 mm
10 nm < W < 100 nm
x
y
Graphene nanoribbon theory partial list
Dk y 
W
W
E  vF k x  (n / W ) 2
2
Zigzag ribbons

Egap~ hvF Dk ~ hvF/W
Scaling of Energy Gaps in Graphene Nanoribbons
Eg (meV)
100
10
Eg = E0 /(W-W0)
P1
P2
P3
P4
D1
D2
1
0
30
60
W (nm)
90
Han, Oezyilmaz, Zhang and Kim PRL (2007)
Top Gated Graphene Nano Constriction
SEM image of device
Top gate
drain
Hf-oxide
drain
source
top gate
source
graphene
graphene
1 mm
30 nm wide x 100 nm long
SiO2
Back gate
75
25
10-2
VBG (V)
G (e2/h)
50
OFF
10-1
10-3
0
10-4
-25
10-5
-50
10-6
-75
-8
-4
0
VLG (V)
4
8
G (e2/h)
10-7 10-5 10-3 10-1
-8
-4
0
VLG (V)
4
8
Graphene Nanoribbons Edge Effect
Crystallographic Directional Dependence
Son, et al, PRL. 97, 216803 (2006)
Eg (meV)
40
20
2mm
0
Rough Graphene Edge Structures
0
30
60
q (degree)
90
Localization of Edge Disordered Graphene Nanoribbons
Querlioz et al., Appl. Phys. Lett. 92, 042108 (2008)
See also:
Gunlycke et al, Appl. Phys. Lett. 90 (14), 142104 (2007).
Areshkin et al, Nano Lett. 7 (1), 204 (2007)
Lherbier et al, PRL 100 036803 (2008)
Transport ‘gap’
Graphene Electronics: Challenges
Pros:
High mobility
tunability of band gaps
High on-off ratio
High critical current density
Small channel length
Small gate capacitance
Large Fermi velocity
This can be turned into advantage:
doping site, functionality, and etc…
Con:
Controlled growth
Edge control
Graphene Electronics: Conventional & Non-conventional
Conventional Devices
FET
Band gap engineered
Graphene nanoribbons
Graphene quantum dot
(Manchester group)
Nonconventional Devices
Graphene Veselago lense
Cheianov et al. Science (07)
Graphene Spintronics
Graphene psedospintronics
Son et al. Nature (07)
Trauzettel et al. Nature Phys. (07)
Non-local Spin Transport and Spin Coherence Length
Spin Relaxation Length ~ 2 mm @ RT
Beyond Simple Spin Transport in Graphene
Coherent Electron Wave Function Manipulation
Carbon Nanotube Superlattice
Pd (under HfO2)
SWCNT
(under HfO2)
3
0.2
0.0
1.0
1.5
Pd (over HfO2)
2
1
2.0
Top Gate (V)
1
HfO2 on SiO2/Si+
1 mm
Pd (under HfO2)
-54
Conductance (mS)
Top Gate (V)
4
dI/dV (mS)
Purewal, Takekosh, Jarillo-Herrero, Kim (2008)
20 nm
0
-50
-45
-40
60 nm
Back Gate (V)
Kouwenhoven PRL (1992)